TM 5-3810-300-24 & P2
The consumption of alcohol will vary on different vehicles. The main determining factor on a properly installed and
maintained unit is the percentage of time the compressor is in its loaded (compressing air) cycle. Being that the use of
alcohol only occurs when the compressor is compressing air, good maintenance practice should be followed by keeping
leakage within allowable limits, adjusting brakes, etc.
While it is difficult to advise what amount of alcohol each vehicle will use, we can set forth an example that can be used as
a guide in determining if the alcohol evaporator is working properly.
Alcohol usage 30 cc to 70 cc (1 oz. to 2 oz.) per hour
(compressor continuously pumping)
Assuming a compressor on a highway tractor-trailer running for 12 hours will be loaded (compressing air) 20% of the total
operating time of 12 hours or roughly 2.5 hours, by multiplying 70 cc (maximum usage of alcohol) by 2.5 hours, we have a
usage of approximately 175 cc (approximately 1/3 to 1/2 pt. 1 pt. 474 cc) of alcohol in 12 hours. It can then be easily seen
by additional calculations that if the compressor is operating a greater percentage of the time more alcohol will be used.
It is recommended that only pure methanol alcohol be used in the air brake system. Bendix-Westinghouse markets this
alcohol under the name "Air Guard" or its equivalent in a correctly installed and maintained alcohol evaporator and proper
draining of all reservoirs in the air brake system is the best insurance against air brake system freeze-ups.
1. Every three months, 900 operating hours, or 25,000 miles:
A. Check to be sure all fittings are tight and bubbles are present in the alcohol when compressor in is compressing
cycle. (If not operating properly, see troubleshooting guide).
2. Every six months, 1800 operating hours, or 50,000 miles:
A. If strainer is present, check to be sure it is clear. Clean or replace if necessary.
3. Every year, 3600 operating hours, or 100,000 miles:
A. Disassemble evaporator and check valve (if so equipped) clean all parts, replacing all gaskets and rubber parts.
With compressor in compressing cycle, bubbles should be evident in alcohol. If air bubbles are not present, check